{
	// 给类型string取名字叫s
	// 1. 别名
	// 2. 建立了新的类型
	type s = string

	let a: string = '123'

	let b: s = '123'

	// let arr1: (number|string)[] = [1,'a']

	// let arr2: (number|string)[] = [1,'a']

	type Ns = (number | string)[]

	let arr1: Ns = [ 1, 'a' ]

	let arr2: Ns = [ 1, 'a' ]

	// let arr2: Ns = [ 1, 'a', false ]
}
